1. Field of the Invention
The invention relates to a cam mechanism through which rotating torque supplied to an input shaft is converted into a compound rotational and axial movement of an output shaft.
2. Description of the Related Art
The type of cam mechanism put forth by the invention is often referred to in the art as a xe2x80x9cpick and pressxe2x80x9d mechanism or xe2x80x9cautomatic tool change unit. xe2x80x9cFIGS. 10 and 11 provide two views of this type of cam mechanism currently known in the art. Roller gear cam 3 is fixedly mounted to input shaft 2. Turret 4 incorporates cam followers 4a that ride between tapered ribs 3a of roller gear cam 3. Turret 4 is rotatably driven by the torque supplied by roller gear cam 3 to cam followers 4a. Output shaft 5 is attached to turret 4 by means of a sliding splined joint that allows the output shaft to be rotatably driven by the turret while axially sliding within the turret.
Moreover, endless channel cam 3b is provided on one face of roller gear cam 3. This structure provides a mechanism by which input shaft 2 is able to impart a reciprocating movement to swing arm 6 by locating one end of the swing arm within the rotating channel cam, and pivotably attaching the other end of the swing arm to output shaft 5. A mechanism is thus created through which the rotating movement of the channel cam is converted to a compound rotating and reciprocating movement of the output shaft. In applications where this cam mechanism is used as part of a tool exchange unit, a tool exchange arm is attached to the end of output shaft 5. The compound action generated by the cam mechanism first rotates the support arm to a position in front of the tool magazine, raises the arm to grip a tool in the magazine, drops the arm to remove the tool, and then rotates the arm in the opposite direction to bring the tool to the exchange position at the lathe, milling machine, machining center, or other like machine. The cam mechanism then raises the arm again, and finally drops the arm to complete the tool change cycle. This cycle is repeated whenever a tool change operation is executed.
This structure, wherein cam followers 4 are located so as to follow the contours of tapered rib 3a, necessitates that the rotating axis of turret 4 be oriented horizontally at a right angle in relation to the vertically oriented rotating axis of roller gear cam 3. The rotating axes of input shaft 2 and output shaft 5 are also relatively disposed at the same right angle. Moreover, swing arm 6 must be located adjacent to roller gear cam 3. Swing arm 6 incorporates base part 6a that is rotatably supported by housing 7, and centrally positioned cam follower 6b that rides within channel cam 3b. This structure necessitates that cam follower 6d, located on end 6c of the swing arm, forms a direct movable connection with flange joint 5a on output shaft 5.
In other words, output shaft 5 must provide a part to which turret 4 can be installed as means of imparting a rotating movement to the output shaft from ribs 3a, and must also include flange joint 5a through which an axially reciprocating movement can be imparted to the output shaft from swing arm 6. In this structure, a substantial space must be provided along the output shaft between turret 4 and flange joint 5a as means of allowing the swing arm to operate in a region separate from the turret. As a result, housing 7 must be fabricated to necessarily large dimensions to provide space for the swing arm to operate at a distance from turret 4 that will not interfere with the operation of turret 4. As illustrated in FIG. 11, housing 7 must incorporate extension housing 7a as means of providing the aforesaid space for the axial movement of output shaft 5 and swing arm 6. Because of the need to incorporate extension chamber 7a into housing 7, the housing becomes relatively large, thus posing various design difficulties in regard to incorporating the cam mechanism into a compact automatic tool change system and/or metal working machine.
The cam mechanism structure proposed by the invention provides adequate space for the reciprocating operation of the swing arm while effectively eliminating restrictions on the placement of the turret part that imparts the rotational movement to the output shaft, thereby allowing the entire cam mechanism to be made to smaller external dimensions.
The cam mechanism invention is comprised of a rotatable roller gear cam fixedly attached to a rotatable input shaft, a turret part rotatably located adjacent to and rotatably driven by the roller gear cam, a cam part formed on one face of the roller gear cam, a reciprocating swing arm located adjacent to and movably joined to the cam part, an output shaft to which the turret part is connected by means of an axially sliding spline joint so as to allow the output shaft to be rotatably driven by the turret part while the output shaft axially sliding thereon, an output shaft joint part formed on the output shaft, a slide rail part located adjacent to the turret part and oriented in an axial direction in relation to the output shaft, and a slider part capable of transferring a reciprocating movement of the swing arm to the output shaft by means of a movable connection between the swing arm and one end of the slider part, and a movable connection between the output shaft joint part and the other end of the slider part.
The reciprocating swinging movement of the swing arm is converted to the axial movement of the output shaft by means of the slider part, the output shaft is thus driven by the slider in the same axial direction as the slider. The use of the slider to transfer and convert the reciprocating swinging movement of the swing arm to the axial movement of output shaft results in a structure that eliminates the previous design restriction of locating the output shaft joint so as to not interfere with the movement of the turret. The structure put forth by the invention allows the range of swing arm movement to be established with a greater degree of latitude. For example, the invention makes possible a larger swing arm stroke within a housing that is no bigger than that used for a conventional cam mechanism. Conversely, the invention makes possible a cam mechanism that can provide the same swing arm stroke as that of the conventional type, but with the cam mechanism encapsulated within a smaller, more compact housing.
Moreover, the cam mechanism invention is structured so as to include a housing that supports a rotating movement of the input shaft and a compound rotating and axial movement of the output shaft. The roller gear cam incorporates tapered ribs formed on its radial perimeter, and an endless cam channel (corresponding to the cam part) formed on one of its lateral radial surfaces. The turret part incorporates radially protruding cam followers that extend to and within a contoured groove delineated by the tapered ribs on the roller gear cam. The swing arm is rotatably supported by the housing and incorporates two cam followers, one cam follower movably connected to the endless cam channel and the other movably connected to the slider part. The output shaft joint part is a grooved ring-type joint comprised of two flanges radially extending from a circumference of the output shaft.
The swing arm is characterized by an enlarged center section in which a curved slot, formed to a width slightly larger than a diameter of the input shaft, is provided as means of preventing the swing arm from contacting the input shaft when the swing arm traverses through its range of movement.
The slider is comprised of a base part and top part. The base part incorporates an elongated rounded hole whose long axis runs in a direction 90 degrees relative to a slider""s direction of movement, and is movably connected to the swing arm. The top part incorporates an attached cam follower that movably connects to the output shaft joint part.
A tool exchange arm is installed to the output shaft as means of intermittently connecting the cam mechanism to tools to be exchanged. An approximate center of the tool exchange arm connects to one end of the output shaft. Tool gripping clamps are provided at each end of the arm as means of gripping tools. The rotating movement of the output shaft revolves the tool exchange arm while the axial movement of the shaft imparts a simultaneous lifting and falling movement to the arm in the axial direction of the output shaft. The roller gear cam and channel cam are designed to provide a desired timing of these rotational and lifting-falling axial movements in a manner that best effects a tool change operation for a specific application.